Lockout/Tagout Program w/ PLC Output

What have you done in the past to ensure that a PLC output is no longer "hot" in an outside electrical panel?

I do not want to turn off the PLC and stop all other functions of my process, and I want my operators to know exactly how to isolate every form of voltage if they are working inside of a panel. Some of these panels have up to five sources of voltage and I am working on documentation to isolate every single one for our LOTO program.

Right now there is not manual disconnect or fuse that we can pull inside the PLC panel for the output, I suppose this might be the only way?

I sometimes use a relay or contactor to isolate the voltage supplying an output card as well as motors, etc. I wire the coil to the e-stop loop so the contactor drops out when the e-stop is activated, removing power to the output card(s). Your scenario will dictate if this is desired at every card or not.

Rube said:

I sometimes use a relay or contactor to isolate the voltage supplying an output card

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I agree, it's all in how you wire and isolate your supply voltage to the card, work that's done upfront in the design. Notice how many (think Micrologix) PLC's will have multiple but isolated V+ supplies on the same card or module.

LiftStation_18 said:

What have you done in the past to ensure that a PLC output is no longer "hot" in an outside electrical panel?

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I have seen cases where the outside panel had a 3-phase power feed plus a single-phase PLC monitoring circuit. In this situation you can find disconnect switches with a mechanically linked auxiliary contact for the PLC hot wire in addition to the power contacts.

AGill said:

......Notice how many (think Micrologix) PLC's will have multiple but isolated V+ supplies on the same card or module.

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And RELAY output cards on other platforms...

We use MCR's as well
+1 all

Relays or emergency stop do not meet the requirements of lockout/tagout. Straight from OSHA:

Energy isolating device. A mechanical device that physically prevents the transmission or release of energy, including but not limited to the following: A manually operated electrical circuit breaker; a disconnect switch; a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors, and, in addition, no pole can be operated independently; a line valve; a block; and any similar device used to block or isolate energy. Push buttons, selector switches and other control circuit type devices are not energy isolating devices.

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Timbert said:

Relays or emergency stop do not meet the requirements of lockout/tagout. Straight from OSHA:

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Even e-stops with lockout mechanism?

fredz0003 said:

Even e-stops with lockout mechanism?

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Unless the e-stop is installed so that it counts as "a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors." i.e. the e-stop switch directly disconnects all power from the machine it doesn't qualify according to OSHA.

Even if it did there are other machine safety standards that, at best, highly discourage the practice as emergency stop devices should only be used for their intended purpose which is to stop the machine in an emergency.

It used to be common but hasn't been allowed for years even though you can still find lockout devices for emergency stop pushbuttons.

fredz0003 said:

Even e-stops with lockout mechanism?

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There is an OSHA interpretation from 1999 that allows "Monitored Power Systems" as sufficient for certain lockout-required tasks. That letter is here:
https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=22838

This is covered on the page 3-32 of the much longer (136-page) OSHA directive here:
https://www.osha.gov/OshDoc/Directive_pdf/CPL_02-00-147.pdf

To the best of my knowledge these are still in force; however, decisions such as these are guided by proper hazard and risk assessments and up to the system designer.

Mispeld said:

This is covered on the page 3-32 of the much longer (136-page) OSHA directive here:
https://www.osha.gov/OshDoc/Directive_pdf/CPL_02-00-147.pdf

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Here is a quote from the above directive (p 3-32):

"The automotive industry designs some processes with Monitored Power System
(MPS) control systems meeting the control reliability and control component
failure protection requirements of the American National Standards for machine
tools (ANSI B11.19-1990) and manufacturing systems/cells (ANSI B11.20-1991).
Although control circuits are not energy isolating devices, as defined by the
standard, the use of MPS which meet the above referenced ANSI standards would
provide effective safeguarding alternative methods, which constitute effective
alternative protection. Thus, such an MPS may be used to protect employees who
are performing minor tool changes and adjustments, and other minor servicing
activities, which take place during normal production operations, provided that
other remaining elements of §1910.147(a)(2)(ii) exception are met. Refer to the
December 16, 1999 letter to the UAW/General Motors Department for additional
details."

Mispeld said:

There is an OSHA interpretation from 1999 that allows "Monitored Power Systems" as sufficient for certain lockout-required tasks. That letter is here:
https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=22838
[/URL]

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Very important to note that even that OSHA interpretation states "Since the MPS relies on electrical control circuits to isolate potentially hazardous energy, and the standard specifically excludes such control circuits in the definition of "energy isolating devices" (1910.147(b)), application of the MPS alone would not constitute compliance with the requirements of §1910.147." Further, it also only allows such a system to be used during minor servicing [§1910.147(a)(2)(ii)]. The minor servicing exemption is a very narrow loophole in lockout/tagout. An MPS is only seen as alternative means of protection in this very narrow loophole, anything else, such as the original poster's "working inside of a panel", still requires a true energy isolating device.

Good catch...I blew right past the LOTO part...

Timbert said:

The minor servicing exemption is a very narrow loophole in lockout/tagout. An MPS is only seen as alternative means of protection in this very narrow loophole, anything else, such as the original poster's "working inside of a panel", still requires a true energy isolating device.

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Yes, very narrow and not intended for general maintenance as implied by the original post.

i did use wincc (HMI) create a button and name it as tagout .this button provide with password where only maintenance personal and manager level carried it..once they press the button it shut down the wanted out ( create ladder as N/C) and i fix relay to indicate which panel (stater Been tagout) .after that maintenace personal will do lockout at Panel stater panel and a signal back to PLC as input and massage appear on HMI mention been lockout by maintenance personal.

even when operator accidently click it it wont start the stater board or energize the output.